Fig. 2.

Comparison of cis- and trans-splicing: In cis-splicing, pair bases U1 small nuclear ribonucleoprotein (snRNP) are in the 5′ SL [?] and U2 snRNPs are in the break point, while intron breaks two exons are connected. In trans-splicing, a 5′-splice site on the mRNA for binding to U1 snRNP is absent. Instead, a 5′-splice site produced by the donor SL snRNP interacts with U2 in the 3′-splice site. The splice leader connects to the next exon. (http://www.wormbook.org/chapters/www_transsplicingoperons/transsplicingoperons.pdf)